b. x-5/921 + x-7/919 + x-9/917 < x-17/909 + x-18/908 + x-19/907

b) x−5921+x−7919+x−9917<x−17909+x−18908+x−19907⇔x−926921+x−926919+x−926917−x−926909−x−18908−x−19907<0⇔x−9261921−1909+1919−1908+1917−1907<0       (1)

Ta có

1921<1909⇔1921−1909<01919<1908⇔1919−1908<01917<1907⇔1917−1907<0

⇒1921−1909+1919−1908+1917−1907<0⇒(1)⇔x−926>0⇔x>926

Vậy x > 926